多对多查询的模型

用户表和角色表的关系为，一个用户有多个角色，一个角色被多个用户使用。

多对多查询的需求：查询所有用户的同时查询出该用户对应的所有角色。

如果图片无法查看，请看这里

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多对多查询的语句

对应的 sql 语句：

select u.id,u.username,r.id,r.rolename from user u left join sys_user_role ur on u.id=ur.userid
inner join sys_role r on r.id= ur.roleid

查询结果如下：

创建 Role 实体，修改 User 实体

User

public class User {private Integer id;private String username;// 代表当前用户具备那些订单private List<Order> orderList;// 代表当前用户具备的那些角色private List<Role> roleList;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public List<Order> getOrderList() {return orderList;}public void setOrderList(List<Order> orderList) {this.orderList = orderList;}public List<Role> getRoleList() {return roleList;}public void setRoleList(List<Role> roleList) {this.roleList = roleList;}@Overridepublic String toString() {return "User{" +"id=" + id +", username='" + username + '\'' +", orderList=" + orderList +", roleList=" + roleList +'}';}
}

Role

public class Role {private Integer id;private String rolename;@Overridepublic String toString() {return "Role{" +"id=" + id +", rolename='" + rolename + '\'' +'}';}
}

UserMapper 添加接口方法

/*** 查询所有用户以及对应的角色* @return*/
public List<User> findAllUserAndRole();

配置 UserMapper.xml

<resultMap id="userRoleMap" type="com.terwergreen.pojo.User"><result property="id" column="id"></result><result property="username" column="username"></result><collection property="roleList" ofType="com.terwergreen.pojo.Role"><result column="rid" property="id"></result><result column="rolename" property="rolename"></result></collection>
</resultMap><select id="findAllUserAndRole" resultMap="userRoleMap">select u.id,u.username,r.id,r.rolename from user u left join sys_user_role ur on u.id=ur.useridinner join sys_role r on r.id=ur.roleid
</select>

测试结果

==>  Preparing: select u.id,u.username,r.id as rid,r.rolename from user u left join sys_user_role ur on u.id=ur.userid inner join sys_role r on r.id=ur.roleid
==> Parameters: 
<==    Columns: id, username, rid, rolename
<==        Row: 1, lucy, 1, CTO
<==        Row: 2, tom, 1, CTO
<==        Row: 1, lucy, 2, CEO
<==        Row: 2, tom, 2, CEO
<==      Total: 4
User{id=1, username='lucy', orderList=null, roleList=[Role{id=1, rolename='CTO'}, Role{id=2, rolename='CEO'}]}
User{id=2, username='tom', orderList=null, roleList=[Role{id=1, rolename='CTO'}, Role{id=2, rolename='CEO'}]}

知识总结

MyBatis 多表配置方式:

一对一配置:使用做配置

一对多配置:使用 + 做配置

多对多配置:使用 + 做配置

本文代码地址

mybatis-multitable

文章更新历史

2022/05/04 feat:初稿